1. Field of the Invention
The present invention relates to an apparatus for setting a target regulation voltage of a vehicle alternator mounted on a vehicle such as a passenger car or a truck.
2. Description of Related Art
There is known a voltage control apparatus for a vehicle alternator, which is configured to detect a rotational speed of the vehicle alternator, calculates a first-order delay of the rotational speed of the vehicle alternator, determines a running state of the vehicle on the basis of difference between the detected rotational speed and the calculated first-order delay, and changes a target regulation voltage of the vehicle alternator depending on the determined running state of the vehicle. For example, refer to Japanese Patent Application Laid-open No. 11-252997. According to such a voltage control apparatus, it is possible to control a vehicle alternator while detecting the running state of a vehicle without provision of specific terminals and cables for connection with external devices, which may cause malfunction of the voltage control apparatus due to poor connection with the external devices.
However, the voltage control apparatus described in the above Patent Document may make an erroneous determination on the running state of the vehicle depending on variation of the rotational speed of the vehicle alternator when a shift change is performed. That is because, since a change in gear ratio is caused by the shift change, increase (or decrease) of the rotational speed of the vehicle alternator does not necessarily mean that the vehicle is in the accelerating state (or in the decelerating state). Furthermore, since the running state of the vehicle is determined from the difference between the detected rotational speed of the vehicle alternator and its first-order delay, the timing at which the running state of the vehicle is determined to have changed may be too late when the vehicle changes from the accelerating state (or decelerating state) to the normal speed (constant-speed state). If such an erroneous determination or late determination is made, fuel consumption is increased, because it is not possible to set the target regulation voltage to an optimum value depending on the running state of the vehicle. In addition, since the voltage control apparatus is located near the vehicle alternator, and accordingly it is susceptible to heat or magnetism from the vehicle alternator, accuracy of setting the target regulation voltage may be lowered.